EP0545307B1 - Process for the preparation of mono-isopropylnaphtalene - Google Patents

Description

The present invention relates to a process for the preparation of monoisopropylnaphthalene (MIPN) by alkylation of naphthalene with zeolites of the faujasite type, the cations of which are exchanged for alkaline earth metal ions, as catalysts.

2-Monoisopropylnaphthalene (2-MIPN) is a valuable intermediate for the production of 2-naphthol by the Hock process. In the conventional process for the preparation of 2-naphthol, the Na salt of 2-naphthalenesulfonic acid is generally converted to 2-naphtholate in a baking melt, from which 2-naphthol is released by subsequent acidification. This process produces a large amount of salts. This disadvantage is largely avoided with the Hock process.

In addition to the monoalkylated products, the alkylation of naphthalene also produces double and triple and, with higher conversions, even higher alkylated naphthalenes. 1- and 2-MIPN are present in the monoisopropylnaphthalene fraction.

In the diisopropylnaphthalene fraction (DIPN), 2,6-diisopropylnaphthalene (2,6-DIPN) is also a valuable intermediate for many highly refined products. For example, it serves as a starting material for the production of 2,6-naphthalenedicarboxylic acid, 2,6-dihydroxynaphthalene and 6-hydroxy-2-naphthalenecarboxylic acid. These compounds are used as monomers for high performance polymers.

In practice, the need for 2-MIPN is much greater than the amount of 2,6-DIPN required for the production of monomers because of the larger amount of 2-naphthol being produced. It is therefore desirable to control the alkylation in such a way that a high selectivity to MIPN and at the same time a high proportion of 2-MIPN in the MIPN fraction is achieved.

It is known that a wide variety of acidic catalysts can be used for the alkylation of naphthalene to MIPN and also DIPN. In the alkylation with Friedel-Crafts catalysts, such as AlCl₃ or BF₃, salts are formed during workup and the catalyst is destroyed. In addition, resin-like compounds form in the course of the reaction, which interfere with the workup. The separation of the products from the catalyst is usually complex. The catalysts are very corrosive and continuous processes are difficult to implement. For this reason, attempts have been made for some time to replace this type of catalyst with solid acids.

DE-PS 2 644 624 describes a process for the preparation of 2-MIPN using H₃PO₄ / SiO₂. The naphthalene must be used in large excess in order to avoid the formation of multi-alkylated products. The naphthalene conversion is limited to a maximum of 60%. The unreacted naphthalene is separated off and returned to the alkylation. Subsequent isomerization of the reaction mixture is necessary in order to obtain a sufficiently high proportion of 2-MIPN. When using acid-activated montmorillonite (DE-OS 2 208 363) or perfluorinated sulfonic acid resins (US Pat. No. 4,288,646), excess naphthalene must be used in order to avoid the formation of large amounts of multiply alkylated products. The low degree of conversion of naphthalene in all of these processes is a considerable disadvantage.

In other works, the possibility of shape-selective catalysis is used to produce the 2-alkyl- and 2,6-dialkylnaphthalenes. Shape selective catalysis means that the dimensions of the molecules involved in the reaction or Transition states are of the same order of magnitude as the catalyst pores. The course of the reaction can be influenced by steric constraints. For example, the alkylation of naphthalene with methanol with zeolites of the ZSM-5 type can be obtained with high selectivity, the slim β-isomers (2-methyl and 2,6-dimethylnaphthalene) (e.g. D. Fraenkel et al., J Catal. 110 (1987) 123-132 and EP-OS 280 055). However, the naphthalene conversion is also limited in these processes because the diffusion of the bulky molecules through the zeolite pores is severely hindered.

In the process of EP-OS 317 907, a dealumized mordenite zeolite was used for the alkylation of naphthalene with propene. A naphthalene conversion of 97.3% was achieved. The yield of DIPN was 68%, of which 50% consisted of 2,6-DIPN. No statements were made about the yield of MIPN and the composition of this fraction. A dealumized mordenite zeolite is also used in the process according to WO 90/03961 for the selective production of 2,6-DIPN. It is stated that this type of zeolite makes the proportion of 2,6-DIPN in the DIPN fraction larger than the proportion in thermodynamic equilibrium and the ratio of 2,6- / 2,7-DIPN greater than 1,2. For example, with 27% conversion of naphthalene, the proportion of 2,6-DIPN 70% and the ratio of 2,6- / 2,7-DIPN 3,0 and the ratio of MIPN / (DIPN + TIPN) 5, 1. If the turnover increases to 78%, the share of 2,6-DIPN increases to 62% and the ratio of 2,6- / 2,7-DIPN to 2,6 and the ratio of MIPN / (DIPN + TIPN) to 1 , 1 from. No information is given on the composition of the MIPN Group.

These examples show that mordenite catalysts strongly suppress the formation of MIPN compared to DIPN with increasing naphthalene conversion.

Faujasites have also been used as catalysts for the alkylation of naphthalene. US Pat. No. 3,251,897 and German Pat. No. 1,468,982 describe the use of Y zeolites which are exchanged with rare earth metal ions and / or protons for the alkylation of naphthalene. The naphthalene conversion was however low and the catalysts only had a short service life. In DE-PS 1 468 982 it is found that Ca²⁺- and Mg²⁺-exchanged X- and Y-zeolites do not catalyze the alkylation of aromatics, such as the ethylation of benzene, while the X- and. Exchanged with ions of the rare earth metals Y zeolites are very active for this reaction.

EP-A 338 292 and EP-A 432 132 describe the reaction of naphthalene with propene on dealuminated Y zeolites (SiO₂ / Al₂O₃ = 10 to 350) in the proton form in the presence of decalin and with hydrogen as the carrier gas. At 220 ° C and a naphthalene conversion of approx. 50%, the selectivity for MIPN is between 68 and 75%, for DIPN between 24 and 30% and for triisopropylnaphthalenes (TIPN) between 1.5 and 3%. 2-MIPN's share of the MIPN is between 91.5 and 93.5%. No statements are made about the composition of the DIPN. The alkylation of MIPN with a proportion of 93% of 2-MIPN to DIPN is also described. The share of 2,6-DIPN in the DIPN fraction is about 40%. A disadvantage of this process is that large amounts of the high-boiling inert diluent have to be separated from the product mixture during workup.

The object of the present invention was to provide a process for the preparation of MIPN by alkylation of naphthalene which does not have the disadvantages described above and which, in particular with a high conversion of naphthalene, has the highest possible selectivity to MIPN with a high proportion of MIPN delivers to the MIPN Group.

According to the invention, this is achieved by using zeolites of the faujasite type, the cations of which are exchanged for alkaline earth metal ions, as catalysts. Simple alkylated products with a high proportion of 2-MIPN are formed with high selectivity.

The invention now relates to a process for the preparation of monoisopropylnaphthalene by alkylation of naphthalene with the aid of zeolites of the faujasite type as catalysts, which is characterized in that the cations of the zeolites are exchanged with ions of the alkaline earth metals.

Zeolites are crystalline aluminosilicates. Si and Al atoms are tetrahedrally surrounded by O atoms. The tetrahedra are linked via common O atoms and form a crystal structure that is defined by defined pores and cavities (cf. D.W. Breck, Zoelite Molecular Sieves, John Wiley & Sons, (1974), pp. 29-185).

Zeolites of the faujasite type, the cations of which are exchanged for alkaline earth metal ions, are suitable for the process according to the invention. The structure of these zeolites is characterized by cuboctahedra (sodalite units), which are linked together by double six-membered rings. A cubic lattice is formed in which large cavities (supercages) are three-dimensionally connected by pores. The pores are delimited by 12 Si or Al atoms and have a diameter of 0.74 nm. The supercages have a diameter of 1.3 nm. Of all zeolites, the faujasites have the widest pores and cavities (DW Breck , loc. cit.). They therefore only exert steric constraints on very large molecules and transition states.

It is surprising that the desired high selectivity to the MIPN can be achieved with this type of zeolite. The mordenite catalyst described in EP-A 317 907, which is used in many works as a shape-selective catalyst for the reaction of mononuclear aromatics, such as 1-methyl-2-ethylbenzene (e.g. SM Csicsery, in Zeolite Chemistry and Catalysis, JA Rabo, ed ., ACS Monograph 171 (1976), pp. 680-713) and has pore sizes of 0.65 x 0.70 nm (Atlas of Zeolite Structure Types, DH Olsen and WM Meier, ed., Butterworths (1990) ), leads to a much stronger formation of DIPN. This also applies to other zeolites whose pores are narrower than those of faujasites, such as beta or EU-1 zeolites. Zeolites of the beta type have a three-dimensional pore system. The pore radii are 0.57 x 0.75 nm and 0.56 x 0.65 nm (JB Higgins et al., Zeolites 8 (1988), pp. 446-452). The pores of EU-1 zeolites are limited only by 10 Si or Al atoms and have a diameter of 0.41 x 0.57 nm. However, the pores have large lateral bulges (Atlas of Zeolite Structure Types, DH Olsen and WM Meier , Ed., Butterworths (1990)). In the examples, some results of the alkylation on the different zeolites are compared. Comparative experiments with lanthanum-exchanged Y zeolites showed that they are active with regard to the alkylation reaction. However, by-products (especially tetralin and isopropyltetraline as well as high-boiling compounds) have been detected to a large extent in the alkylate.

The zeolites of the faujasite type used in the invention are commercially available and can be prepared by known processes with SiO₂ / Al₂O₃ ratios between 2 and about 7. The aluminum-rich faujasites are called X-zeolites (SiO₂ / Al₂O₃ = 2 to 3) and the lower-aluminum Y-zeolites (SiO₂ / Al₂O₃ = 3 to 7). By subsequent dealumination, however, higher SiO₂ / Al₂O₃ ratios can also be achieved. The aluminum content can be reduced in various ways. Some methods are e.g. in J. Scherzer, Catalytia Materials; Relationship between Structure and Reactivity, ACS Symp. Ser. 248 (1984), pp. 175-200. Faujasites with SiO₂ / Al₂O₃ ratios between 4 and 400, preferably between 5 and 200, are particularly suitable for the process according to the invention.

In order to convert the zeolite into a catalytically active, ie acidic form, the Na⁺ ions present are exchanged for ions of the alkaline earth metals by ion exchange. In addition to the alkaline earth metal ions, small amounts of rare earth metal ions and / or ammonium ions or protons can also be present in the zeolite. It is expedient that at least 50% of the negative grid charges are compensated for by ions of the alkaline earth metals. At least 95% of the exchangeable Na⁺ ions are preferably replaced by ions of the alkaline earth metals. All water-soluble salts, in particular chlorides and nitrates, are generally suitable as salts of the alkaline earth metals which are used for ion exchange. The zeolite is then through Dehydration (and deammonization in NH₄⁺ forms) at 200 to 800 ° C, preferably at 250 to 550 ° C converted into the catalytically active form. Faujasites (ie X- and Y-zeolites) which are exchanged with Ca²⁺ and Mg²⁺ ions are particularly suitable as catalysts. They are referred to below as CaY or CaX or MgY or MgX.

The alkylation reaction can be carried out in the gas phase, but preferably in the liquid phase. Examples of alkylating agents which can be used are i-propanol, propene, i-propyl chloride and bromide. In the gas phase reaction, it is preferred to react naphthalene with propene or i-propanol. In the case of alkylation in the liquid phase, the use of propene is preferred.

The reaction temperature is advantageously between about 100 and 500 ° C, preferably between about 150 and 300 ° C. An increased pressure is favorable for the course of the alkylation, in particular if alkylation is carried out with propene. The reaction can be carried out at negative pressure, atmospheric pressure or higher pressure, e.g. up to about 100 bar, preferably between about 2 and 20 bar.

The alkylation in the liquid phase can be carried out in any suitable apparatus, the simplest being discontinuously in a stirred tank with powdered catalyst suspended in molten naphthalene. The process can also be carried out continuously in the liquid phase. Propene is then passed through the suspension at reaction temperature or pressed to the desired pressure. Inert gases such as nitrogen can also be used to achieve the reaction pressure.

Based on the mass of naphthalene used, it is particularly expedient for batchwise operation to use between about 0.1 and 50% by weight of catalyst, preferably between about 1 and 10% by weight. Depending on the reaction conditions and the desired conversion, the reaction time can be between about 0.5 h and several days, in particular between 2 and 10 h. After done The zeolite can be separated from the reaction mixture in a simple manner, for example by filtration.

In principle, all apparatus suitable for gas phase reactions can be used to carry out the reaction in the gas phase. Technically, the easiest to handle is a fixed bed flow reactor. The catalyst can be installed in the form of pellets in the reactor. For the production of the pellets, the zeolite can be pressed together with a binder such as Al₂O₃ or SiO₂ or binder-free. Oxides, hydroxides or hydroxychlorides of aluminum and the oxides of silicon, titanium and zirconium and clay materials are particularly suitable as binders.

The naphthalene can be metered into the reactor in the molten state or dissolved in an inert solvent and evaporated in front of the catalyst bed, or it can be converted into the gaseous state before the reactor and thus passed into the reactor. The reaction is preferably carried out without using solvents.

I-propanol can be dosed in the same way as naphthalene. Propene is introduced in gaseous form. The reactants can be used alone or as a mixture with a gas which is inert to the reaction, such as hydrogen or nitrogen. However, it is preferred to carry out the reaction without inert solvents or gases. The products are condensed after leaving the reactor.

The molar ratio of naphthalene to the alkylating agent is expediently in the range from about 0.1 to 10, preferably from about 0.2 to 1.2, in the case of continuous operation.

The residence time of the reactants is generally between about 0.05 and 20 s, preferably between 1 and 10 s. The space velocity (LHSV = liquid hourly space velocity = ml insert per ml catalyst volume and hour) can preferably be set in the range of 0.1 and 5 h⁻¹, the range between 0.5 and 2 h⁻¹ being particularly favorable.

The catalyst can be used several times for the reaction. If it is deactivated, it can be regenerated again by calcining in an oxidizing atmosphere, preferably in air, at about 350 to 800 ° C., preferably at about 500 to 600 ° C.

The proportion of 2-MIPN in the product mixture can be increased in a further process step by isomerization, also using acidic faujasites as catalysts, up to a maximum of the equilibrium proportion (at 200 ° C the proportion of 2-MIPN in the MIPN fraction is in equilibrium at approx. 95%). For this reason, the goal of achieving a high proportion of 2-MIPN in the MIPN fraction is subordinate to the goal of high selectivity to MIPN. The proportion of 2,6-DIPN can also be increased within the DIPN fraction by subsequent isomerization. In equilibrium at 200 ° C it is approx. 42%. Another advantage of the process is that two valuable products (2-MIPN and 2,6-DIPN) can be produced at the same time.

The higher alkylated naphthalenes formed in the alkylation can be converted back to MIPN by transalkylation with naphthalene. The transalkylation is a side reaction of the isomerization and can therefore take place in the same process step as the isomerization. Alkaline earth metal exchanged zeolites of the faujasite type are also active for the isomerization and transalkylation of isopropylnaphthalenes.

The product mixture can first be separated into unreacted naphthalene, MIPN, DIPN and TIPN by distillation. Unreacted naphthalene can either be used again for the alkylation or can be fed into the isomerization / transalkylation stage together with the more alkylated reaction products. 2-MIPN can be obtained from the MIPN fraction by crystallization, possibly from a solvent such as methanol or i-propanol, or by sorption on molecular sieves (see, for example, DE-OS 2 517 591). The filtrate enriched in 1-MIPN can be converted back into a mixture rich in 2-MIPN by isomerization on various zeolites (see, for example, US Pat. No. 4,026,959). 2,6-DIPN can also be separated from the DIPN fraction by crystallization (see, for example, EP-PS 216 009). Adsorptive separation is described, for example, in JP-OS 01 199 921. The rest of the DIPN fraction largely freed from 2,6-DIPN can be used together with

Naphthalene can be converted back to MIPN by transalkylation. The following usual cleaning steps can be used to further clean 2-MIPN and 2,6-DIPN to the desired degree.

Examples

The Na⁺ ions of the Y zeolites used (SiO₂ / Al₂O₃ = 5.4) were exchanged for the corresponding cations by ion exchange using alkaline earth metal chlorides (or rare earth metal nitrates in comparative example V4). The zeolite was treated with 10 times the amount of 10% aqueous solutions of these salts under reflux for 6 to 7 hours. This exchange was repeated 3 times. In example 1, 85% of the sodium ions were exchanged for calcium ions and in example 2 70% of the sodium ions for magnesium ions.

Y zeolites with less aluminum were dealuminated with SiCl₄ by the method of H. Beyer, described in H. Beyer and I. Belenykaya, Stud. Surf. Sci. Catal. 5 (1980), pp. 203-210. By repeated boiling with 10 times the amount of 1N HCl, these low-aluminum zeolites were dealuminated even further. After this treatment, the zeolites were calcined at 550 ° C.

The comparative zeolites with other structures were prepared by hydrothermal synthesis according to the regulations from the literature. Zeolite beta was obtained according to Example 7 from US Pat. No. 3,308,069 with an SiO₂ / Al₂O₃ ratio of 23 in the gel synthesized. Mordenite crystallized in a modified beta synthesis according to the above-mentioned regulation, the equimolar amounts of tetraethylammonium bromide and NaOH being used instead of tetraethylammonium hydroxide. The crystallization of EU-1 zeolites is described in GW Dodwell et al., Zeolites 5 (1985), pp. 153-157. After crystallization, the zeolites were filtered off, dried and calcined in air at 550 ° C. Then they were treated twice with 10% aqueous NH₄NO₃ solution and calcined again. In addition, like the Y zeolites, mordenite was treated once with 1N HCl for one hour and also calcined.

Examples 1 and 2 and comparative examples V1 to V4 were carried out in a stirred tank. The zeolite was dried at 300 ° C for 1 hour before the reaction and then suspended in powder form in 128 g of molten naphthalene. 5% by weight of zeolite, based on naphthalene, were used. Propene was passed through the suspension at 6.5 l / h at atmospheric pressure. The reaction temperature was 200 ° C. The test results are summarized in the table.

The results of the naphthalene alkylation with the zeolites according to the invention show that high selectivities to MIPN S _MIPN (over 90 mol% at X _N = 20 mol% naphthalene conversion) can be achieved.

The MIPN selectivities achieved with HMordenite and HBeta (V2 and V3), on the other hand, are significantly reduced. HEU-1 (V1) also delivers a high MIPN selectivity, but the proportions of 2-MIPN A _2-MIPN in the MIPN fraction are significantly lower than the proportions achieved in Examples 1 and 2. As described in the literature, a high proportion of 2,6-DIPN A _{2,6-DIPN is} obtained with HMordenite, but in addition to the low selectivity to MIPN, only a significantly lower conversion is achieved after 6 hours of testing. Zeolites (V4) exchanged with lanthanum show a low selectivity to MIPN due to the many by-products.

Claims (11)

1. A process for the preparation of monoisopropylnaphthalene by alkylation of naphthalene with the aid of zeolites of the faujasite type as catalysts, wherein the cations of the zeolites have been replaced by alkaline earth metal ions.
2. The process as claimed in claim 1, wherein the alkaline earth metal ions are Mg²⁺ and/or Ca²⁺ ions.
3. The process as claimed in claim 1 or 2, wherein the zeolite has a SiO₂/Al₂O₃ ratio of from 4 to 400, preferably from 5 to 250.
4. The process as claimed in one or more of claims 1 to 3, wherein at least 50% of the negative lattice charges in the zeolites of the faujasite type are compensated by alkaline earth metal ions.
5. The process as claimed in one or more of claims 1 to 3, wherein at least 95% of the exchangeable Na⁺ ions have been replaced by alkaline earth metal ions.
6. The process as claimed in one or more of claims 1 to 5, wherein the reaction is carried out in the liquid phase.
7. The process as claimed in one or more of claims 1 to 6, wherein the reaction is carried out at temperatures of from 100 to 500°C, preferably of from 150 to 300°C.
8. The process as claimed in one or more of claims 1 to 7, wherein the reaction is carried out under a pressure of up to 100 bar, preferably from 2 to 20 bar.
9. The process as claimed in one or more of claims 1 to 8, wherein the alkylating agent used is i-propyl bromide, i-propyl chloride, propene or i-propanol.
10. The process as claimed in one or more of claims 1 to 9, wherein, in the case of a continuous procedure, naphthalene is used in a molar ratio of 0.1 to 10, preferably of 0.2 to 1.2, with respect to the alkylating agent.
11. The process as claimed in one or more of claims 1 to 10, wherein, in the case of a discontinuous procedure, from 0.1 to 50% by weight, preferably from 1 to 10% by weight, of catalyst are used with respect to the mass of naphthalene employed.